Structure and thermotropic properties of 1,3-dipalmitoyl-glycero-2-phosphocholine.
Structure and thermotropic properties of 1,3-dipalmitoyl-glycero-2-phosphocholine.
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1,3-二棕榈酰-甘油-2-磷酸胆碱的结构和热致性质。
DOI：
10.1016/s0022-2836(83)80231-9
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发表时间：
1983
影响因子：
5.6
通讯作者：
Shipley,GG
中科院分区：
文献类型：
--
作者：
Serrallach,EN;Dijkman,R;deHaas,GH;Shipley,GG
通过X射线衍射和差示扫描量热法研究了水合1,3-二棕榈酰-甘油-2-磷酸胆碱(β-DPPC)的结构和热致性质。在-3°C下长时间储存后，差示扫描量热法加热扫描在27°C和37°C下表现出吸热转变，转变焓分别为ΔH= 9·1和10·5 kcal/mol β-DPPC（1 cal = 4·184 J）。冷却后，高温转变是完全可逆的，而低温转变则不然。为了重新获得低温转变的全部热函，需要在低温下长时间孵育水合 β-DPPC，这表明低温形式的亚稳定性。 X 射线衍射研究表明，从 -3°C 加热平衡的 β-DPPC 时会出现三种不同的层状相：（1）低于 18°C，水合（14 mol 水/mol β-DPPC）“结晶”双层相 Lc，具有有序烃链堆积模式和双层周期 d= 58 Å； (2) 30°C 至 35°C 之间，水合（22 mol 水/mol β-DPPC）凝胶相 Lβ，具有六角链堆积且 d= 47 Å；小双层周期性、1/4·2 Å−1 处尖锐、对称的广角反射、界面处每摩尔 β-DPPC 的面积约为 80 Å2、电子密度分布和使用带状电子密度模型计算的结构因子表明该相存在烃链交错； (3) 高于 37°C，高度水合（48 mol 水/mol β-DPPC）液晶双层相，Lα，d= 65 Å。之前的核磁共振和中子衍射研究表明，在 β-DPPC 中，甘油主链采用平行于双层表面的方向，而不是在 α-DPPC 中通常垂直的方向。与位置异构体 α-DPPC 相比，这种构象可能导致分子内链分离增加，从而导致 β-DPPC 的分子堆积、水合和热致行为发生变化。
The structure and thermotropic properties of hydrated 1,3-dipalmitoyl-glycero-2-phosphocholine (β-DPPC) have been studied by X-ray diffraction and differential scanning calorimetry. After prolonged storage at −3°C, differential scanning calorimetry heating scans exhibit endothermic transitions at 27°C and 37°C, with transition enthalpies, ΔH= 9·1 and 10·5 kcal/mol β-DPPC, respectively (1 cal = 4·184 J). Upon cooling, the high temperature transition is completely reversible, whereas the low temperature transition is not. Prolonged incubation of hydrated β-DPPC at low temperatures is necessary in order to regain the full enthalpy of the low temperature transition, indicating metastability of the low temperature form. X-ray diffraction studies indicate three different lamellar phases upon heating equilibrated β-DPPC from −3°C: (1) below 18°C, a hydrated (14 mol water/mol β-DPPC) “crystalline” bilayer phase, Lc, with an ordered hydrocarbon chain-packing mode and a bilayer periodicityd= 58 Å; (2) between 30°C and 35°C, a hydrated (22 mol water/mol β-DPPC) gel phase, Lβ, with hexagonal chain-packing andd= 47 Å; hydrocarbon chain interdigitation in this phase is suggested by the small bilayer periodicity, a sharp, symmetric wide-angle reflection at 1/4·2 Å−1, an area per mol β-DPPC at the interface of ∼80 Å2, electron density profiles and structure factor calculations using strip electron density models; (3) above 37°C, a highly hydrated (48 mol water/mol β-DPPC) liquid crystalline bilayer phase, Lα, withd= 65 Å.Previous nuclear magnetic resonance and neutron diffraction studies have suggested that in β-DPPC the glycerol backbone adopts an orientation parallel to the bilayer surface, in contrast to its usual perpendicular orientation in α-DPPC. This conformation presumably results in an increasedintramolecular chain separation, with consequent changes in the molecular packing, hydration and thermotropic behavior of β-DPPC, compared to its positional isomer α-DPPC.